The human Y chromosome is the smallest chromosome in the human genome and contains about 30 Mb of euchromatin. Because of its genetic simplicity, the actual informative sequence may be as little as 10-14 Mb and has been estimated to contain about 200-350 functional genes. Most of these genes are either related to male physiology or members of polygenic traits. Recently the First International Workshop on Human Y Chromosome Mapping was held on April 2-5,1994 at Hughes Hall, Cambridge, England. This workshop was attended by 64 scientists from 8 countries, including 15 participants from the United States. Numerous goals have been achieved through the Cambridge Workshop, including the generation of consensus deletion and physical contig maps of the entire euchromatin and subregions, localization of 14 genes and many new STSs on these maps, definition of X-Y homology, comparative mapping of human and mouse Y chromosomes and evaluation of positional cloning strategies for EST collection from this chromosome. Despite these advances, more work is needed to achieve the ultimate goal of determining the complete genetic information of this chromosome. First, many of the regional deletion and physical contig maps in YACs, PI clones and cosmids have to be incorporated into the overall physical contig map, thereby constructing a higher resolution physical map of the euchromatin. As evidenced by the tremendous interests in large-scale positional cloning techniques, additional ESTs in terms of cDNAs and trapped exons are being isolated from this chromosome in many laboratories. These ESTs will needed to be incorporated into a first generation transcription map of the human Y chromosome. Based on the above developments, we propose to conduct a Second International Workshop on Human Y Chromosome to be held on September 17- 20,1995 at the Asilomar Conference Center, Pacific Grove, California. This workshop will focus on the construction of consensus deletion and physical contig maps of the entire euchromatin and the subregions, on advances of X-Y homology and comparative mappings, and the assembly of a first- generation transcription map of the human Y chromosome. It will be an important opportunity for investigators in this field to assemble and present their results, reconcile and discuss about differences in their findings, and interact and collaborate with each others in studies of mutual interests. The proposed workshop will be an important landmark towards the ultimate goal of a complete determination of the genetic content on the human Y chromosome.